The present invention relates to infrared detecting elements adapted to detect infrared rays utilizing a change in physical properties thereof due to heat such as pyroelectricity, change in resistance with varying temperature or thermoelectromotive force. More particularly, it relates to an infrared detecting element which assures a substantial rise in temperature in response to incident infrared rays of a very small thermal responsiveness with less crosstalk, and which is suitable quantity and offers excellent sensitivity and for high integration and is used solely or in an array arrangement.
Conventional infrared detecting elements include quantum detectors and thermal detectors. The quantum detectors include one utilizing photoconduction, one utilizing photovoltaic effect and the like, and generally offer excellent responsiveness and sensitivity. However, they must be cooled to temperatures lower than the temperature of liquid nitrogen (77 K.) for use and, hence, the major disadvantages thereof include difficulties in downscaling and handling and their high price. By contrast, the thermal detectors include one utilizing pyroelectricity, one utilizing a change in resistance with varying temperature, one utilizing thermoelectromotive force, and the like, and generally offer less sensitivity and responsiveness than the quantum detectors. Nevertheless, they offer great advantages in that they need no cooling, allow downscaling and lightening and offer a low price.
Objectives common to these thermal detectors in enhancing the sensitivity thereof include:
(1) to make the detection part exhibit a large rise in temperature in response to incident infrared rays of a very small thermal quantity, i.e., to reduce the thermal capacity of the detection part; PA1 (2) to reduce thermal leakage due to thermal conduction from the detection part to its peripheral portions; PA1 (3) to reduce heat conduction from the element in operation to elements adjacent thereto if the thermal detector is in an array arrangement; PA1 (4) to form the detection part integrally with a signal processing system and; PA1 (5) to make the array of elements have a sufficient strength. PA1 defining a concave portion into the substrate at a location where the infrared detecting member is to be formed; PA1 filling the concave portion with an easy-to-etch material made of a material to be easily etched or a material to be easily etched while retaining a porous skeleton having a low thermal conductivity; PA1 sequentially stacking the support member and the infrared detecting member on the easy-to-etch material, followed by patterning; and PA1 etching the easy-to-etch material to define a cavity portion or to form a porous member. PA1 forming a convex portion on a surface of the substrate at a location where the infrared detecting member is to be formed, the convex portion being formed of an easy-to-etch material made of a material to be easily etched or a material to be easily etched while retaining a porous skeleton having a low thermal conductance; PA1 sequentially stacking the support member and the infrared detecting member on the substrate including the convex portion, followed by patterning; and PA1 etching the convex portion to define a cavity portion or to form a porous member. PA1 forming a spacer on a surface of the substrate at a location where the infrared detecting member is to be formed, the spacer being formed of an easy-to-etch material made of a material to be easily etched or a material to be easily etched while retaining a porous skeleton having a low thermal conductance; PA1 forming an intermediate layer made of a material hard to etch having a high thermal conductance on a surface of the substrate at a location where the infrared detecting element is not to be formed; PA1 sequentially stacking the support member and the infrared detecting member on the spacer, followed by patterning; and PA1 etching the spacer to define a cavity portion or to form a porous member. PA1 stacking on a substrate a support member and an infrared detecting member, followed by patterning; PA1 etching a spacer provided between the substrate and the support member or a surface of the substrate lying under the support member to define a cavity portion between the support member and the substrate; and PA1 filling the cavity portion with a porous member forming material, followed by a post-treatment to form a porous member.
Of the thermal detectors, the pyroelectric-type element is considered to offer the highest sensitivity and has been put into practical use in some forms of two-dimensional array detector. A pyroelectric-type, two-dimensional array detector described in, for example, "Bulletin of Ceramic Process", Vol. 41, 1989, pp. 205 to 217, is fabricated by mechanically polishing a pyroelectric ceramic wafer to a thickness of several tens .mu.m and forming grooves into the wafer by ion milling for thermal isolation of individual detection parts. Top electrodes of the detection parts of this detector is connected to a signal processing circuit by means of a metallic bump to achieve electrical connection therebetween.
On the other hand, a pyroelectric-type, two-dimensional array detector described in, for example, "ITEJ Technical is Report", Vol. 13, 1989, p. 7, is fabricated by forming a thin film on an MgO substrate to form detection parts, forming a protective film of polyimide over the resulting surface and completely removing the portion of the MgO substrate lying under the detection parts by etching so as to retain the MgO substrate in the form of a frame lying on the outermost detection part side as supporting the overall array of elements in a bridged fashion. In this detector the elements in each column of the array are connected in series and further electrically connected to an external signal processing circuit at an end portion of the column.
The former detector, however, involves problems in that: (1) there is a limitation in making the ceramic wafer thin, namely, in reducing the thermal capacity of each detection part or the size thereof since the ceramic wafer is machined; (2) high fabrication precision is needed for obtaining stable sensitivity; (3) the use of bump connection causes the productivity to decrease and the mechanical strength of the detector to be lowered; and the like. Similarly, the latter detector suffers problems in that: (1) the complete removal of the substrate under the two-dimensionally arrayed detection parts by etching results in a structure with low strength; only one signal processing circuit is provided to each column of elements, resulting in a disadvantageous signal-to-noise ratio; (3) in association with the low mechanical strength, the detection parts are likely to vibrate, so that the noise based on the piezoelectric property of the pyroelectric material is likely to occur; and the like.
It is, therefore, an object of the present invention to overcome the foregoing problems and to provide a thermal-type infrared detecting element having a thin film detecting part with less thermal capacity and less thermal conduction to peripheral portions and a method for fabricating the same.
Another object of the present invention is to provide a thermal-type infrared detector apparatus with less crosstalk wherein detecting elements of the same type as above are arranged in an array.
A further object of the present invention is to provide a thermal-type infrared detector apparatus wherein the detection part and a signal processing circuit are integrally formed.